IM doing an animation project at uni (deadline next week) and I need a background track. I've found one I like and perfected it in Audition. However when I try and import it into After Effects, the quality of the playback is extremely quiet and fuzzy.

You want to avoid using compressed formats in production. MP3 may be an OK delivery format but all wave files for video should be at least 49Khz 16bit wav or aif files. If you are sending anything else to AE you are not getting the best audio.